1. Field of the Invention
The present invention relates to the so-called Triplate type microstripline applicable to a transmission line for microwaves, a filter, a microwave integrated circuit (MIC) employing such elements and the like.
2. Description of the Prior Art
FIGS. 7 and 8 illustrate conventional microstriplines generally employed as transmission lines for MICs.
The microstripline as shown in FIG. 7 comprises a dielectric substrate 101 of ceramic for example, which is provided with a ground electrode 102 on one major surface and a line electrode 103 on the other major surface. Although such a microstripline is simple in structure, the same exhibits large conductor loss and electromagnetic field leakage.
On the other hand, the microstripline member as shown in FIG. 8 is of the so-called Triplate type, which comprises two dielectric substrates 106 and 107 of ceramic for example, provided on major surfaces thereof with ground electrodes 104 and 105, and provided with a line electrode 108 interposed between the same. This microstripline is smaller in conductor loss than that of FIG. 7, and has substantially no electromagnetic field leakage.
In the microstripline member as shown in FIG. 8, however, a small gap 109 shown by the dotted line may occur defined between the line electrode 108 and the dielectric substrate 106 or 107 due to warpage of the dielectric substrate 106 or 107 or displacement thereof with respect to the other one upon superposition, to degrade the circuit constants (characteristic impedance, effective dielectric constant etc.) of the microstripline, leading to unstable characteristics of a filter or a circuit employing the microstripline member.